1. Field of the Invention
The present invention relates to a golf club head, more particularly to a joint structure of a metal part made of a metal material and a FRP part made of a fiber reinforced resin.
2. Description of the Related Art
In recent years, golf club heads made of a metal material and fiber reinforced resin have been proposed. These heads can save the weight thereof on the basis of the small specific gravity of the resin. Further, the saved weight can be allocated, for example, in the sole portion or the like, and can improve degree of freedom in the weight allocation design or the like.
However, in the head mentioned above, an adhesive strength tends to be short in a joint portion between the metal material and the resin. Accordingly, there has been conventionally proposed various techniques of improving a rigidity of the joint portion.
For example, in Japanese Unexamined Patent Publication No. 2003-205055, as shown in FIGS. 15(A) and 15(B), there is described a head “a” comprising a metal member b provided with an opening “o” in a crown portion and made of a metal material, and a FRP member “c” arranged in the opening and made of a fiber reinforced resin. The FRP member c includes edge pieces c1 and c2 bonded to an inner side and an outer side of an edge portion j of the metal member b. However, in this structure, a crack tends to be generated from a portion between the edge pieces c1 and c2 of the bifurcated inner and outer FRP members, due to a great impact force at a time of striking a ball.
Further, in the document mentioned above, as shown in FIGS. 16(A) and 16(B), there has been proposed a structure in which a plurality of through holes f are intermittently provided in the edge portion j of the metal member b, and a cord g joining the edge pieces c1 and c2 of the inner and outer FRP members and made of a fiber reinforced resin is arranged in the through holes f. However, a shear force due to the impact force at a time of striking the ball tends to act on a joint interface between the edge pieces c1 and c2 and the cord body f. Accordingly, it is desired to further improve the adhesive strength.